Low-cost spectrometry system for end-user food analysis

ABSTRACT

A compact spectrometer is disclosed that is suitable for use in mobile devices such as cellular telephones. In preferred embodiments, the spectrometer comprises a filter, at least one Fourier transform focusing element, a micro-lens array, and a detector, but does not use any dispersive elements. Methods for using the spectrometer as an end-user device for performing on site determinations of food quality, in particular, by comparison with an updatable database accessible by all users of the device, are also disclosed.

CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.14/356,144, filed on May 2, 2014, entitled “Low-Cost Spectrometry Systemfor End-User Food Analysis”, which is a national stage entry ofPCT/IL2012/000367, filed on Oct. 31, 2012, entitled “Low-CostSpectrometry System for End-User Food Analysis”, which claims priorityof U.S. Provisional Application Ser. No. 61/555,043, filed on Nov. 3,2011, each of which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to low-cost spectrometry systems. In particular,it relates to systems that do not use gratings but that have sufficientsensitivity and resolution to perform spectroscopic analysis, inparticular via a distributed network, of substances (including complexmixtures), in particular foodstuffs, that are in the possession of theindividual consumer.

BACKGROUND OF THE INVENTION

Food safety is a consumer issue of long standing. Even if a particularitem was fresh at the time of its transportation to the point of sale oreven at the time the end user obtains it, its freshness and safety atthe actual time of use cannot be guaranteed. Thus, a method that wouldenable the end user to check a foodstuff for contamination immediatelyprior to consumption would be of major benefit to the consumer.Non-invasive methods, i.e. methods that do not involve removal ordestruction of a portion of the food being tested, would be ideal, sincesuch a method would provide ease of use and hence a higher likelihood ofuse.

Spectroscopic methods for determination of food safety meet therequirements of being non-invasive and of being easy in principle touse. There are two major obstacles that need to be overcome before useof such methods by the end user can become routine. The first is thenecessity to provide an appropriate spectrometer. FIG. 1 shows a designof a typical spectrometer 10 known in the art. Light 105 enters throughslit 100, is reflected from first mirror 101 onto a dispersive elementsuch as a grating (103) which directs the light onto a second mirror102. Because the light is dispersed by element 103 according to itswavelength, every pixel of the spectrometer's sensor 104 will beilluminated by a specific wavelength. Spectrometers that use this designare complicated, require precise alignment, are difficult to assembleand are limited in their miniaturization capabilities.

In contrast, a spectrometer suitable for routine consumer use must besmall, rugged, easy to use, and capable of providing spectra ofsufficient quality and resolution that meaningful conclusions about thecontent of the food being tested can be made. The second obstacle isthat foods and their contaminants are in general not simple substances,but complex mixtures of substances that themselves tend to havecomplicated spectra. Thus, for such an end-user system to be useful, itmust incorporate means for real-time analysis of the frequentlycomplicated spectra obtained.

While development of such a spectrometry system would be a boon toend-user determination of food safety, its usefulness would extend farbeyond such a limited use. For example, it could be used in applicationsas diverse as detection of environmental contaminants, remote detectionof explosives or chemical or biological agents, or for remote diagnosisor monitoring of a patient's condition (e.g. blood oxygen or glucoselevels).

There has thus been a considerable effort devoted to development ofcompact spectrometry systems to meet these needs. Some examples ofcompact spectrometry systems known in the art are given here.

U.S. Pat. No. 7,262,839 discloses a compact birefringent interferenceimaging spectrometer. This spectrometer comprises at least one liquidcrystal cell or a micromechanical Fabry-Perot system that is used as atunable filter. In some embodiments, the liquid crystal cell can bedesigned to create a series of bandpass zones. Different wavelengths aretuned across the x-y image field of a two-dimensional detector, enablingcollection of wavelength resolved or spatially resolved spectral data.

U.S. Pat. No. 7,420,663 discloses a portable spectroscopic sensingdevice that is integrated into a mobile communication device such as amobile telephone. The spectrometer uses the sensor associated with thecamera located in the mobile communication device as a detector, and itsconnection with the mobile device allows uploading of the spectralinformation thus obtained to a remote location. The spectroscopicsensing device disclosed is based on a dispersive element such as agrating or prism, with all of the consequent drawbacks of such a device.

U.S. Pat. Appl. 2010/0201979 discloses a system and method forperforming spectral-spatial mapping. Instead of a dispersive elementsuch as a prism or grating, the system disclosed therein uses acylindrical beam volume hologram (CVBH) to disperse the light. Thisdesign has the advantage that no slit or grating is needed, but suffersfrom drawbacks of low throughput and small spectral range. In addition,the expense of the CVBH element precludes its use in a spectrometerintended for consumers.

U.S. Pat. Appl. 2010/0309454 discloses a portable spectrometerintegrated into a wireless communication device. Not only does thespectrometer disclosed therein depend on dispersive elements, but thesystem itself requires the use of a fiber optic cable attached to thewireless communication device to transmit light to the spectrometer,further limiting the ease of use and increasing the cost of the system.

Thus, a compact spectrometer system that can be integrated into aconsumer device such as a cellular telephone while being sufficientlyrugged and low in cost to be practical for end-user spectroscopicmeasurements of suspect items, and a convenient method by which thespectra obtained by such a spectrometer system (in particular those ofcomplicated mixtures such as foodstuffs) can be analyzed and thelikelihood of contamination estimated remains a long-felt yet unmetneed.

SUMMARY OF THE INVENTION

The compact spectrometer system and method herein disclosed are designedto meet this long-felt need. A low-cost, rugged spectrometer with nodispersive elements or moving parts is disclosed, along with a method ofusing cloud computing via a continuously updatable database to analyzedata obtained by the spectrometer and to return the results of theanalysis to the user. The spectrometer system herein disclosed has asubstantially straight optical axis and, in preferred embodiments,comprises no more than 2-4 elements excluding the detector. Thealignment accuracy required between the elements is very low relative tothat of spectrometers of the type illustrated in FIG. 1. The straightoptical axis and small sensor size enable production of spectrometersthat are small enough and economical enough to fit in devices such ascellular phones, and yet have sufficient sensitivity and resolution(typically <10 cm⁻¹) to obtain useful spectra of complex mixtures suchas foodstuffs.

It is therefore an object of the present invention to disclose a compactspectrometer system for obtaining the spectrum of a sample, comprising(a) an optical detector for detecting light emanating from said sample;(b) an optical filter located between said sample and said detector; and(c) a first Fourier transform focusing element, wherein said compactspectrometer system does not contain any dispersive optical elements.

It is a further object of this invention to disclose such a compactspectrometer system, wherein said optical filter is a non-tunablefilter.

It is a further object of this invention to disclose such a compactspectrometer system as defined in any of the above, wherein said firstFourier transform focusing element is disposed between said opticalfilter and said optical detector such that light passing through saidoptical filter is dispersed by said at least one focusing element ontothe light-sensitive surface of said detector.

It is a further object of this invention to disclose such a compactspectrometer system as defined in any of the above, wherein the centerwavelength of said optical filter varies with the incidence angle oflight impinging thereupon.

It is a further object of this invention to disclose such a compactspectrometer system as defined in any of the above, wherein said opticalfilter comprises a plurality of sub-filters with different centerwavelengths.

It is a further object of this invention to disclose such a compactspectrometer system, wherein said optical filter comprises a pluralityof substantially parallel strips, each of which comprises a sub-filter.

It is a further object of this invention to disclose such a compactspectrometer system, wherein said optical filter comprises a pluralityof substantially rectangular areas, each of which comprises asub-filter.

It is a further object of this invention to disclose such a compactspectrometer system as defined in any of the above, wherein said opticalfilter is chosen from the group consisting of (a) Fabry-Perot filter,(b) thin-film filter, and (c) interference filter.

It is a further object of this invention to disclose such a compactspectrometer system as defined in any of the above, wherein said firstFourier transform focusing element is a plano-convex lens disposed suchthat its flat face faces said optical detector and its curved face facessaid optical filter.

It is a further object of this invention to disclose such a compactspectrometer system as defined in any of the above, further comprising asecond Fourier transform focusing element.

It is a further object of this invention to disclose such a compactspectrometer system, wherein said Fourier transform focusing elementsare plano-convex cylindrical lenses disposed such that the flat face ofeach lens faces said optical detector, the curved face of each lensfaces said optical filter, the focal lines of the two lenses areoriented along different axes in the x-y plane, and the focal planes ofsaid Fourier transforming focusing elements substantially coincide.

It is a further object of this invention to disclose such a compactspectrometer system, wherein the focal planes of said Fouriertransforming focusing elements are substantially coincident withlight-sensitive surface of said optical detector.

It is a further object of this invention to disclose such a compactspectrometer system, wherein the focal lines of said Fourier transformfocusing elements are perpendicular.

It is a further object of this invention to disclose such a compactspectrometer system as defined in any of the above, further comprising amicro-lens array.

It is a further object of this invention to disclose such a compactspectrometer system, wherein said micro-lens array is located in thefocal plane of said first Fourier transform focusing element.

It is a further object of this invention to disclose such a compactspectrometer system, wherein said detector is located at a planesubstantially perpendicular to the optical axis such that themicro-lenses form multiple images of said optical filter on said opticaldetector.

It is a further object of this invention to disclose such a compactspectrometer system, wherein said optical filter comprises a pluralityof sub-filters with different center wavelengths.

It is a further object of this invention to disclose such a compactspectrometer system, further comprising a second Fourier transformingfocusing element, wherein said micro-lens array comprises an array ofcylindrical lenses and is located at the focal plane of first of twosaid focusing elements and said optical detector is located at the focalplane of second of two said focusing elements.

It is a further object of this invention to disclose such a compactspectrometer system as defined in any of the above, further comprising adiffuser disposed between said sample and said optical filter.

It is a further object of this invention to disclose such a compactspectrometer system as defined in any of the above, wherein said firstFourier transform focusing element is a lens chosen from the groupconsisting of (a) plano-convex lenses, (b) biconvex lenses, and (c)aspheric lenses, and further wherein said optical filter is locatedbetween said first Fourier transform focusing element and said sample.

It is a further object of this invention to disclose such a compactspectrometer system, wherein said optical filter comprises a pluralityof sub-filters with different center wavelengths.

It is a further object of this invention to disclose such a compactspectrometer system, wherein said plurality of sub-filters is disposedradially about a center point.

It is a further object of this invention to disclose such a compactspectrometer system, wherein said optical filter is in close proximityto said optical detector.

It is a further object of this invention to disclose such a compactspectrometer system as defined in any of the above, wherein said opticaldetector is a two-dimensional image sensor.

It is a further object of this invention to disclose such a compactspectrometer system as defined in any of the above, further comprising alight source adapted to illuminate said sample.

It is a further object of this invention to disclose such a compactspectrometer system, wherein said light source is a laser.

It is a further object of this invention to disclose such a compactspectrometer system, wherein said light source is a light-emittingdiode.

It is a further object of this invention to disclose such a compactspectrometer system, further comprising a focusing system adapted focuslight from said light source at a predetermined location relative tosaid sample.

It is a further object of this invention to disclose such a compactspectrometer system, wherein said focusing system is an autofocussystem.

It is a further object of this invention to disclose such a compactspectrometer system, wherein said focusing system controls the positionof a lens that focuses light produced by said light source onto saidsample.

It is a further object of this invention to disclose such a compactspectrometer system, wherein said focusing system controls the opticalproperties of a lens that focuses light produced by said light sourceonto said sample.

It is a further object of this invention to disclose such a compactspectrometer system, wherein said focusing system comprises a voice-coilmotor.

It is a further object of this invention to disclose such a compactspectrometer system, wherein said focusing system comprises apiezoelectric motor.

It is a further object of this invention to disclose such a compactspectrometer system, wherein said focusing system comprises amicro-electrical-mechanical-system (MEMS) motor.

It is a further object of this invention to disclose such a compactspectrometer system as defined in any of the above, wherein said lightemanating from said sample comprises light scattered by said sample uponillumination.

It is a further object of this invention to disclose such a compactspectrometer system, wherein said spectrum is selected from the groupconsisting of (a) molecular vibrational spectra, (b) molecularrotational spectra, and (c) electronic spectra. In some preferredembodiments of said compact spectrometer system, the spectrum is a Ramanspectrum.

It is a further object of this invention to disclose such a compactspectrometer system, further comprising a second optical filter.

It is a further object of this invention to disclose such a compactspectrometer system, wherein said light scattered from said sample uponillumination comprises light reflected by said sample upon illumination.

It is a further object of this invention to disclose such a compactspectrometer system as defined in any of the above, wherein said lightemanating from said sample comprises light produced by fluorescenceemanating from said sample.

It is a further object of this invention to disclose such a compactspectrometer system as defined in any of the above, further comprisingmeans for communicating with a communication network.

It is a further object of this invention to disclose such a compactspectrometer system, wherein said communication network is a wirelesscommunication network.

It is a further object of this invention to disclose such a compactspectrometer system, wherein said compact spectrometer system isenclosed within a mobile communication device associated with saidcommunication network.

It is a further object of this invention to disclose such a compactspectrometer system, wherein said mobile communication device is acellular telephone.

It is a further object of this invention to disclose such a compactspectrometer system, further comprising a database of spectralinformation in communication with said communication network.

It is a further object of this invention to disclose such a compactspectrometer system, wherein said database is continuously updatable inreal time.

It is a further object of this invention to disclose such a compactspectrometer system as defined in any of the above, further comprising alocal digital processor.

It is a further object of this invention to disclose such a compactspectrometer system, wherein said local digital processor is programmedto perform at least one algorithm chosen from the group consisting of(a) an algorithm for operating said compact spectrometer system; (b) analgorithm for processing raw spectral data obtained by said compactspectrometer system; (c) an algorithm for comparing data obtained bysaid compact spectrometer system with data stored in a database; and (c)an algorithm for transmitting spectral data obtained by said compactspectrometer system to a remote server.

It is a further object of this invention to disclose such a compactspectrometer system as defined in any of the above, further comprisinglocal memory.

It is a further object of this invention to disclose such a compactspectrometer system, wherein said local memory is chosen from the groupconsisting of (a) fixed memory and (b) volatile memory.

It is a further object of this invention to disclose such a compactspectrometer system, further comprising a local database of spectralinformation stored within said local memory.

It is a further object of this invention to disclose such a compactspectrometer system as defined in any of the above, wherein said compactspectrometer system is incorporated into an oven.

It is a further object of this invention to disclose such a compactspectrometer system, wherein said oven is a microwave oven.

It is a further object of this invention to disclose such a compactspectrometer system as defined in any of the above, wherein said compactspectrometer system is incorporated into a refrigerator.

It is a further object of this invention to disclose such a compactspectrometer system as defined in any of the above, further comprisingGPS positioning means for determining the location of said spectrometersystem.

It is a further object of this invention to disclose such a compactspectrometer system as defined in any of the above, wherein said samplecomprises food.

It is a further object of this invention to disclose a method ofobtaining a spectrum of a sample without using dispersive optics,wherein said method comprises: providing a sample; causing lightemanating from said sample to impinge on an optical filter, the centerwavelength of which depends on the angle of incidence of the lightimpinging upon it; passing said light to a first Fourier transformfocusing element; measuring the intensity of light as a function ofposition in a predetermined plane P₁; and converting the intensity oflight as a function of position in said plane P₁ to a spectrum.

It is a further object of this invention to disclose such a method,wherein said step of measuring the intensity of light as a function ofposition in a predetermined plane P₁ comprises measuring the intensityof light as a function of position in a plane substantially coincidentwith the focal plane of said first Fourier transform focusing element.

It is a further object of this invention to disclose such a method asdefined in any of the above, wherein said step of causing lightemanating from said sample to impinge on an optical filter precedes saidstep of passing said light to a first Fourier transform focusingelement, whereby the light passing through said optical filter isangle-encoded according to its wavelength and said light is transformedby said Fourier transform focusing element to spatially encoded.

It is a further object of this invention to disclose such a method asdefined in any of the above, wherein said step of passing said light toa first Fourier transform focusing element precedes said step of causinglight emanating from said sample to impinge on an optical filter.

It is a further object of this invention to disclose such a method asdefined in any of the above, further comprising a step of placing insaid predetermined plane P₁ an image sensor adapted to measure theintensity of light impinging upon said image sensor as a function ofposition.

It is a further object of this invention to disclose such a method asdefined in any of the above, wherein said step of passing said light toa first Fourier transform focusing element comprises a step of passingsaid light to a plano-convex lens, the curved surface of which is facingsaid optical filter.

It is a further object of this invention to disclose such a method asdefined in any of the above, wherein said step of causing lightemanating from said sample to impinge on an optical filter comprises astep of causing light emanating from said sample to impinge on anoptical filter comprising a plurality of sub-filters.

It is a further object of this invention to disclose such a method,further comprising placing a micro-lens array in a predetermined planeP₂ oriented such that each micro-lens samples the optical Fouriertransform formed at said plane P₂, thereby creating a micro-image of theaperture of said optical filter at a predetermined plane P₃, and therebydecomposing the sampling points of said optical Fourier transformaccording to the origin of the light at a particular sub-filter reachingsaid micro-lens.

It is a further object of this invention to disclose such a method,wherein said predetermined plane P₂ is substantially identical to thefocal plane of said first Fourier transform focusing element.

It is a further object of this invention to disclose such a method,further comprising a step of placing an image sensor adapted to measurethe intensity of light impinging upon said image sensor as a function ofposition in said predetermined plane P₃.

It is a further object of this invention to disclose such a method,further comprising placing said plurality of sub-filters along a singleaxis and passing said angle-encoded light through a second Fouriertransform focusing element disposed such that the spatially encodedlight produced by said second Fourier transform focusing element isencoded at an angle relative to the orientation of the spatially encodedlight produced by said first Fourier transform focusing element and suchthat the focal plane of said second Fourier transform focusing elementis substantially identical with said predetermined plane P₃; whereinsaid step placing a micro-lens array between said first Fouriertransform focusing element and said predetermined plane P₃ furthercomprises placing a micro-lens array comprising cylindrical micro-lensesdisposed such that the light passing through said micro-lens array isdisposed in said plane along an axis parallel to said single axis.

It is a further object of this invention to disclose such a method,wherein said step of passing said angle-encoded light to a first Fouriertransform focusing element comprises a step of passing saidangle-encoded light to a first plano-convex cylindrical lens, the curvedsurface of which is facing said optical filter, and said step of passingsaid angle-encoded light through a second Fourier transform focusingelement comprises a step of passing said angle-encoded light to a secondplano-convex cylindrical lens, the curved surface of which is facingsaid optical filter.

It is a further object of this invention to disclose such a method,further comprising placing said micro-lens array in the focal plane ofsaid first Fourier transform focusing element; and placing said opticaldetector in the focal plane of said second Fourier transform focusingelement.

It is a further object of this invention to disclose such a method asdefined in any of the above, further comprising passing said lightthrough a diffuser.

It is a further object of this invention to disclose such a method asdefined in any of the above, further comprising illuminating said samplewith a light source.

It is a further object of this invention to disclose such a method,wherein said step of illuminating said sample comprises illuminatingsaid sample with a light source chosen from the group consisting oflasers and light emitting diodes.

It is a further object of this invention to disclose such a method asdefined in any of the above, wherein said spectrum is selected from thegroup consisting of (a) molecular vibrational spectra, (b) molecularrotational spectra, and (c) electronic spectra. In some preferredembodiments of said method, the spectrum is a fluorescence spectrum. Insome preferred embodiments of said method, the spectrum is a Ramanspectrum.

It is a further object of this invention to disclose such a method asdefined in any of the above, wherein said spectrum is a fluorescencespectrum.

It is a further object of this invention to disclose such a method,further comprising a step of separating the Raman signal from thefluorescence signal.

It is a further object of this invention to disclose such a method,further comprising a step of focusing light emanating from said lightsource to a predetermined location relative to said sample.

It is a further object of this invention to disclose such a method,wherein said step of focusing light emanating from said light sourcecomprises a step of focusing light emanating from said light sourceusing an autofocus system.

It is a further object of this invention to disclose such a method,wherein said step of focusing light emanating from said light sourceusing an autofocus system further comprises analyzing in real time thesignal obtained by said spectrometer; and commanding said autofocussystem accordingly, so that said light is focused to the optimal signalextraction point at the sample.

It is a further object of this invention to disclose such a method asdefined in any of the above, further comprising analyzing the spectrumobtained by comparison with a database of spectral information.

It is a further object of this invention to disclose such a method,wherein said step of analyzing comprises at least one step chosen from(a) comparing said spectrum with spectra in a spectral database; (b)comparing said spectrum with spectra in a spectral database by usingPrincipal Components Analysis; (c) comparing said spectrum with spectrain a spectral database by using Partial Least Squares analysis; and (d)comparing said spectrum with spectra in a spectra database by using aneural network algorithm.

It is a further object of this invention to disclose such a method,further comprising adding said spectrum to said spectral database.

It is a further object of this invention to disclose such a method,further comprising transmitting said spectrum to a remote processingunit; using said remote processing unit to perform said step ofanalyzing; and transmitting the results of said step of analyzing to theuser.

It is a further object of this invention to disclose such a method,wherein said steps of transmitting are performed by transmitting over awireless network.

It is a further object of this invention to disclose such a method,further comprising performing a preliminary analysis of said spectrumobtained in said step of converting the intensity of light as a functionof position in the focal plane of said first Fourier transform focusingelement.

It is a further object of this invention to disclose such a method,wherein said step of performing a preliminary analysis of said spectrumis performed using a local processing unit.

It is a further object of this invention to disclose such a method,wherein said step of performing a preliminary analysis of said spectrumis performed remotely.

It is a further object of this invention to disclose such a method,wherein said step of performing a preliminary analysis of said spectrumfurther comprises at least one step chosen from the group consisting of(a) averaging a plurality of independent measurements; (b) compensatingfor optical aberrations; and (c) reducing detector noise using a noisereduction algorithm.

It is a further object of this invention to disclose such a method asdefined in any of the above, further comprising a step of transmittingto a predetermined remote location the location at which said spectrumis obtained.

It is a further object of this invention to disclose such a method asdefined in any of the above, said step of transmitting to apredetermined remote location the location at which said spectrum isobtained further comprises a step of determining the location at whichsaid spectrum by use of a GPS.

It is a further object of this invention to disclose such a method asdefined in any of the above, wherein said steps of causing lightemanating from said sample to impinge on an optical filter, the centerwavelength of which depends on the angle of incidence of the lightimpinging upon it; passing said light to a first Fourier transformfocusing element; and measuring the intensity of light as a function ofposition in said plane P₁ are performed by using optical elements, allof which are disposed within or upon a mobile communication device.

It is a further object of this invention to disclose such a method,wherein said mobile communication device is a cellular telephone.

It is a further object of this invention to disclose such a method asdefined in any of the above, wherein said steps of causing lightemanating from said sample to impinge on an optical filter, the centerwavelength of which depends on the angle of incidence of the lightimpinging upon it; passing said light to a first Fourier transformfocusing element; and measuring the intensity of light as a function ofposition in said plane P₁ are performed by using optical elements, allof which are disposed within or upon an oven.

It is a further object of this invention to disclose such a method,wherein said oven is a microwave oven.

It is a further object of this invention to disclose such a method asdefined in any of the above, wherein said steps of causing lightemanating from said sample to impinge on an optical filter, the centerwavelength of which depends on the angle of incidence of the lightimpinging upon it; passing said light to a first Fourier transformfocusing element; and measuring the intensity of light as a function ofposition in said plane P₁ are performed by using optical elements, allof which are disposed within or upon a refrigerator.

It is a further object of this invention to disclose such a method asdefined in any of the above, wherein said sample comprises food.

It is a further object of this invention to disclose such a method asdefined in any of the above, wherein said sample comprises medication.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the drawings,wherein

FIG. 1 presents a schematic diagram of a grating-based spectrometeraccording known in the art;

FIGS. 2A-2E present schematic diagrams of the optical layouts of severalnon-limiting embodiments of the compact spectrometer system hereindisclosed;

FIG. 3 presents a schematic illustration of the dispersion of light upona detector according to one embodiment of the compact spectrometersystem herein disclosed;

FIGS. 4A-4D present schematic illustrations of several embodiments ofoptical filters that comprise a plurality of sub-filters for use in thecompact spectrometer system herein disclosed;

FIG. 5 presents a schematic illustration of the extraction of theFourier images in a non-limiting embodiment of the invention hereindisclosed;

FIGS. 6A-6B present block diagrams of compact spectrometersincorporating the invention herein disclosed; and,

FIG. 7 presents a block diagram of one embodiment of the connection ofthe invention herein disclosed to a communication network.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, various aspects of the invention will bedescribed. For the purposes of explanation, specific details are setforth in order to provide a thorough understanding of the invention. Itwill be apparent to one skilled in the art that there are otherembodiments of the invention that differ in details without affectingthe essential nature thereof. Therefore the invention is not limited bythat which is illustrated in the figure and described in thespecification, but only as indicated in the accompanying claims, withthe proper scope determined only by the broadest interpretation of saidclaims.

As used herein, the term “dispersive” is used, with respect to opticalcomponents, to describe a component that is designed to direct light inspace according to its wavelength, and thus to separate spatially thedifferent wavelength components of a polychromatic beam of light.Non-limiting examples of “dispersive” optical elements by thisdefinition include diffraction gratings and prisms. The termspecifically excludes elements such as lenses that disperse lightbecause of non-idealities such as chromatic aberration or elements suchas interference filters that have different transmission profilesaccording to the angle of incident radiation.

Reference is now made to FIG. 2A, which illustrates one non-limitingembodiment of the compact spectrometer system 20 herein disclosed. Thesystem comprises an optical filter 200, a first Fourier transformfocusing element 201, and a detector 204. In preferred embodiments ofthe invention, the first Fourier transform focusing element 201 is aplano-convex lens oriented such that the convex side is facing theoptical filter. The detector is located in a predetermined plane P₁,which in preferred embodiments of the invention is the focal plane ofthe first Fourier transform focusing element.

Optical filter 200 can be of any type known in the art. Non-limitingexamples of suitable optical filters include Fabry-Perot (FP)resonators, cascaded FP resonators, and interference filters. In atypical embodiment of the simplest possible arrangement shown in FIG.2A, a narrow bandpass filter (≦10 cm⁻¹) with a wide blocking rangeoutside of the transmission band (at least 200 nm) can be used. Inpreferred embodiments, the center wavelength (CWL) of the filter varieswith the incident angle of the light impinging upon it.

Detector 204 may be of any suitable type known in the art capable ofdetecting light in the wavelength range of interest; the compactspectrometer system disclosed herein can be used from the UV to the IR,depending on the nature of the spectrum being obtained and theparticular spectral properties of the sample being tested. Because, aswill be explained below, spectra are obtained by measuring the intensityof light as a function of the position in a predetermined plane (e.g.the focal plane of the first Fourier transform focusing element), inpreferred embodiments of the invention, a detector that is capable ofmeasuring intensity as a function of position (e.g. an array detector ora two-dimensional image sensor) is used.

The basic principle of operation of compact spectrometer 20 is asfollows. Light 205 impinges upon optical filter 200. Assuming that light205 is approximately spatially invariant over the area of the opticalfilter (in typical embodiments of the invention, the entrance aperturehas an area of the order of 1 mm²), and that the light impinges upon thefilter at a sufficiently wide range of propagation angles, both of whichare reasonable assumptions, the light passing through the filter isangularly encoded after passing through the optical filter. The firstFourier transform focusing element (201) performs (approximately) aspatial Fourier transform of the angle-encoded light, transforming itinto a spatially-encoded spectrum. That is, the intensity of lightrecorded by the sensor as a function of position (pixel number) on thesensor is correlated to the intensity at wavelength of the lightcorresponding to that position.

Reference is now made to FIG. 3, which illustrates the dispersion oflight on detector 204 for an embodiment in which the detector is a 2-Dimage sensor located in plane P₁ which is substantially coincident withthe focal plane of first Fourier transform focusing element 201, and thefirst Fourier transform focusing element is a lens with radial symmetry.As can be seen in the figure, light of different wavelengths (λ₁, λ₂,λ₃, λ₄, etc.) will arrive at the detector as a series of circles ofdifferent radii proportional to the wavelength. In general, therelationship between the wavelength and the radius of the correspondingcircle will not be linear.

In embodiments in which the light emanating from the sample is notsufficiently diffuse, a diffuser is placed in front of the opticalfilter. Reference is now made to FIG. 2B, which illustrates a typicalembodiment of compact spectrometer system 20 that incorporates adiffuser. Collimated (or partially collimated light) 206 impinges on thediffuser, which then produces diffuse light 205 which then impinges onoptical filter 200.

The use of a single filter, as shown in FIG. 2A, can limit the spectralrange available to the spectrometer. For example, if the angle ofincidence of light is larger than 30°, the system will probably notproduce a signal of sufficient intensity due to lens aberrations and thedecrease in the efficiency of the detector at large angles. For anangular range of 30° and an optical filter CWL of ˜850 nm, the spectralrange available to the spectrometer will be ˜35 nm. This range isinsufficient for many applications such as Raman spectroscopy. Inembodiments with larger spectral ranges, an optical filter that isactually composed of a plurality of sub-filters, in which eachsub-filter has a different CWL and thus covers a different part of theoptical spectrum, is used.

Reference is now made to FIGS. 4A and 4B, which show two non-limitingembodiments of an optical filter that comprises a plurality ofsub-filters. FIG. 4A shows an optical filter in which the sub-filters (8in the embodiment shown) are arranged along a single axis, while FIG. 4Bshows an optical filter in which the sub-filters (9 in the embodimentshown) are tiled in two dimensions.

Depending on the number of sub-filters, the wavelength range accessibleto the spectrometer can reach hundreds of nanometers. In the case of theuse of a plurality of sub-filters, the approximate Fourier transformsformed at the image plane (i.e. one per sub-filter) overlap, and thesignal obtained at any particular pixel of the detector will normallyresults from a mixture of the different Fourier transforms.

In order to separate the signals originating from different sub-filters,a micro-lens array is placed in a predetermined plane P₂ that is locatedbetween the first Fourier transform focusing element and the detector.Such micro-lens arrays are well-known in the art, e.g. in Plenopticcameras. In preferred embodiments, the micro-lens array plane P₂ issubstantially coincident with the focal plane of the first Fouriertransform focusing element, and the detector plane P₃ is substantiallycoincident with the plane that includes the image of the optical filtercreated by the micro-lens array. Reference is now made to FIG. 2C, whichshows schematically the optical layout of an embodiment of the compactspectrometer 20 that incorporates a micro-lens array 203 disposed suchthat it is in the focal plane of first Fourier transform focusingelement 201 and such that detector 204 lies in the plane that includesthe image of the optical filter created by the micro-lens array.

In these embodiments, each micro-lens thus acts as a “super-pixel” thatseparates the light impinging upon it into components corresponding tothe plurality of Fourier transformations produced by the plurality ofsub-filters. Each micro-lens creates an image on the detector of theaperture of the optical filter. The “micro-image” thus formed representsthe contribution to the signal from each part of the lens aperture (i.e.the optical filter) to the “super-pixel” covered by the micro-lens.Reference is now made to FIG. 5, which illustrates the decomposition ofthe signal by the micro-lens array into the separate Fourier transformedsignals. Each micro-lens samples the overall Fourier image and eachsample is then decomposed according to the signal origin at opticalfilter 200, enabling extraction of the Fourier image for eachsub-filter.

In the particular embodiment illustrated in FIG. 5, optical filter 200comprises a plurality of sub-filters aligned along a single axis. Lightimpinging on the Fourier transform focusing elements from three of thesub-filters (indicated in the figure as 2100, 2200, and 2300) leads tothree different signals (210, 220, and 230, respectively) that aredispersed by the micro-lens array on the detector. The micro-lens arrayis disposed such that the light is dispersed on the detector along anaxis parallel to the axis on which the sub-filters are aligned.

Reference is now made to FIG. 2D, which illustrates the optical layoutof a preferred embodiment of compact spectrometer system 20 thatincludes a cylindrical micro-lens array. In these embodiments, a secondFourier transform focusing element 202 (in preferred embodiments, bothof the Fourier transform focusing elements are plano-convex cylindricallenses with the convex side facing the detector) is placed between thefirst Fourier transform focusing element and the micro-lens array.Second Fourier transform focusing element 202 is oriented such that itsfocal line is not aligned with that of the first Fourier transformfocusing element. In preferred embodiments, the two focal lines areperpendicular. The second Fourier transform focusing element is placedsuch that the detector lies in its focal plane.

Table 1 provides a summary of the properties of the components of thecompact spectrometer system in a typical embodiment. Note that inpreferred embodiments, the f-numbers of the Fourier transform lenses andthe micro-lenses are identical. The wavelength resolution of thisembodiment is <10 cm⁻¹.

TABLE 1 Parameter Value comments Length of sides of system 1 mm apertureis equal to total filter aperture size sub-filter width 0.125 mm 8sub-filters First Fourier transform 4.2 lens diameter 2 mm, focal lengthlens f-number 6 mm sensor pixel size 5 μm micro-lens f-number 4.2 lensdiameter 40 μm, focal length 169.7 μm; array pitch = diameter Wavelengthrange per 27.67 nm sub filter Overall wavelength range 221.4 nm =numberof sub-filters × wavelength range of each sub- filter

In some embodiments of the invention, an additional filter is placed infront of the compact spectrometer system in order to block light outsideof the spectral range of interest (i.e. to prevent unwanted light fromreaching the detector).

Reference is now made to FIG. 2E, which illustrates the optical layoutof another embodiment of the invention herein disclosed. In thisembodiment, optical filter 200 is located in close proximity to thedetector, and first Fourier transform focusing element 201 is a radiallysymmetric biconvex, plano-convex, or aspheric lens; that is, acylindrical lens is not used in this embodiment. Diffuse light 205entering the spectrometer system is Fourier-transformed by first Fouriertransform focusing element 201. Unlike the previously describedembodiments, there is no angular wavelength encoding before the Fouriertransform focusing element.

In this embodiment, the light that impinges upon the filter is directedin a wide range of angles, each spot on the detector corresponding to adifferent angle of incidence. As in the previous embodiments, theoptical filter is designed such that its CWL depends on the angle ofincidence. Thus, each concentric ring on the image will include only anarrow part of the spectrum of the light reaching the spectrometersystem.

In embodiments in which the spectral range covered by a single opticalfilter is insufficient, as with the previous embodiments, an opticalfilter comprising a plurality of sub-filters with differing CWLs isused. Two non-limiting embodiments of the design of such optical filtersare shown in FIGS. 4C and 4D. As the light reaching the detector inthese embodiments is axially symmetric, the sub-filters are disposedabout a center point. In the embodiments illustrated in FIGS. 4C and 4D,there is a gap in the center of filter 200. Since in general thevariation of wavelength with angle of incidence is small at smallincidence angles, not using the central part of the image is notexpected to affect the quality of the spectrum significantly.

The embodiment illustrated in FIG. 2E involves a trade-off of addedsimplicity against reduced performance. The advantage of the embodimentillustrated in FIG. 2E is that the number of parts in the system can bereduced, since the optical filter can be fabricated on top of, or atleast mounted on, the detector. On the other hand, each spot created onthe image plane is composed of many optical rays (equivalent to manyplane waves) whose incident angle is not identical. Specifically, eachspot is composed of a ray bundle impinging on the detector over range ofangles, where the center of this range is the angle created by the lineconnecting the center of the lens and the spot on the image and the lineconnecting the center of the lens and the center of the image. Dependingon the f-number of first Fourier transform focusing element 201, thisangle, which is inversely proportional to the f-number, can vary from afraction of a degree to several degrees. Each ray in the ray bundle willexperience a different filtering function, thus reducing the spectralresolution. For non-critical applications, the reduction in spectralresolution will be compensated for by the decreased complexity and costof this embodiment of the system.

In some embodiments of the invention, the measurement of the sample isperformed using scattered ambient light. In most cases, the scatteredambient light will not be sufficiently intense to provide a spectrum ofsufficiently high quality. Therefore, in preferred embodiments of theinvention, the compact spectrometer system incorporates a light source.The light source can be of any type (e.g. laser or light-emitting diode)known in the art appropriate for the spectral measurements to be made.

Because of its small size and low complexity, the compact spectrometersystem herein disclosed can be integrated into a mobile communicationdevice such as a cellular telephone. It can either be enclosed withinthe device itself, or mounted on the device and connected to it by anywired or wireless means for providing power and a data link known in theart. By incorporating the spectrometer system into a mobile device, thespectra obtained can be uploaded to a remote location, analysisperformed there, and the user notified of the results of the analysis,as described in detail below. The spectrometer system can also beequipped with a GPS device so that the location of the sample beingmeasured can be reported.

Because of its small size and low cost, the spectrometer system hereindisclosed can also be integrated into kitchen appliances such as ovens(particularly microwave ovens), food processors, refrigerators etc. Theuser can then make a determination of the safety of the ingredients inreal time during the course of food storage and preparation.

Reference is now made to FIG. 6, which illustrates two non-limitingembodiments of spectrometers for obtaining spectra of a sample 30 thatincorporate the compact spectrometer system herein disclosed. Thespectrometer incorporates, in addition to compact spectrometer system20, a light source 60. In some embodiments, the light source may be alaser; in other embodiments, it may be a light-emitting diode (LED). Thewavelength(s) and intensity of the light source will depend on theparticular use to which the spectrometer will be put. The spectrometeralso includes a power source (e.g. a battery or power supply) 40 andprocessing and control unit 50. In the embodiment shown in FIG. 6A, thespectrometer additionally incorporates I/O optics 70, while in theembodiment shown in FIG. 6B, in place of the I/O optics of the previousembodiment, optical filters are included, one between the light sourceand the sample, and the other between the sample and compactspectrometer system 20. One skilled in the art will recognize that thespectrometers herein disclosed can be adopted, with proper choice oflight source, detector, and associated optics, for a use with a widevariety of spectroscopic techniques. Non-limiting examples includeRaman, fluorescence, and IR or UV-VIS reflectance spectroscopies.Because, as described above, compact spectrometer system 20 can separatea Raman signal from a fluorescence signal, in some embodiments of theinvention, the same spectrometer is used for both spectroscopies.

As mentioned above, a second problem for adapting spectroscopictechniques for determination of food safety is the complicated nature ofthe substance being tested and hence the complicated analysis that isnecessary. In particular, if the intended user is an individualconsumer, the use of the spectrometry system must be no more complicatedthan “point and shoot,” and the analysis provided to the user withoutany extensive activity on his or her part.

In some embodiments of the invention, the spectrometer system comesequipped with a memory with a database of spectral data stored thereinand a microprocessor with analysis software programmed in. The memorycan be volatile in order that the user's own measurements can beincorporated into it. In other embodiments, the database and/or all orpart of the analysis software is stored remotely, and the spectrometersystem communicates with it via a network (e.g. a wireless network) byany appropriate method known in the art. In preferred embodiments inwhich the database is located remotely, it is continuously updatable. Inthis manner, each measurement made by a user of the spectrometerincreases the quality and reliability of future measurements made by anyuser.

In a typical method of use of the compact spectrometer, the userilluminates the sample, a spectrum of which is to be obtained. Thespectrum is then obtained as described above. The spectrum is thenanalyzed using any appropriate analysis method. Non-limiting examples ofspectral analysis techniques that can be used include PrincipalComponents Analysis, Partial Least Squares analysis, and the use of aneural network algorithm to determine the spectral components. Thespectrum is thus analyzed to determine whether the spectrum of thecomplex mixture being investigated contains components consistent withthe spectrum of a substance, mixture of substances, or microorganism,the presence of which is undesirable, and from the intensity of thesecomponents in the spectrum, whether their concentration is high enoughto be of concern. Non-limiting examples of such substances includetoxins, allergens, decomposition products, or harmful microorganisms. Inpreferred embodiments of the invention, if it is deemed likely that thesample is not fit for consumption, the user is provided with a warning.

In preferred embodiments of the invention, it is connected to acommunication network that allows users to share the informationobtained in a particular measurement. An updatable database located inthe “cloud” (i.e. the distributed network) constantly receives theresults of measurements made by individual users and updates itself inreal time, thus enabling each successive measurement to be made withgreater accuracy and confidence as well as expanding the number ofsubstances for which a spectral signature is available.

Reference is now made to FIG. 7, which presents a block diagram of thecommunication environment of the method disclosed herein for using thesystem disclosed herein. A probe, comprising a light source, compactspectrometer system 20 and associated optics has a logical connection toa platform comprising some or all of the hardware and software describedabove. The probe system may include additional components for providinginformation to the user. Non-limiting examples of such componentsinclude a GPS to link the food sampling with the location at which thesampling was performed; a camera for recording the visual impression ofthe sample; and sensors for measuring such environmental variables astemperature and humidity.

The block diagram shown in FIG. 7 also shows the logical links to thelocal or remote databases discussed above. In various embodiments of theinvention, the conversion of the raw intensity data to a spectrum may beperformed either locally (with a processor and software supplied withthe spectrometer system) or remotely. Heavier calculations for morecomplicated analyses will in general be performed remotely.

In embodiments that incorporate remote data analysis, the datatransferred to the remote system may include one or more of raw detectordata; pre-processed detector data or post-processed detector data inwhich the processing was performed locally; or the spectrum derived fromthe raw detector data. These examples are not intended to be limiting,and are merely given to illustrate typical embodiments of the invention.

In some embodiments of the invention, the following signal processingscheme is used. First, an image or a series of images is captured by theimage sensor in the spectrometer mentioned above. The images areanalyzed by a local processing unit. This stage of analysis may includeany or all of image averaging, compensation for aberrations of theoptical unit, reduction of detector noise by use of a noise reductionalgorithm, or conversion of the image into a raw spectrum. The rawspectrum is then transmitted to a remote processing unit; in preferredembodiments, the transmission is performed using wireless communication.

The raw spectrum is then analyzed remotely. First, noise reduction isperformed. Then, in embodiments in which a Raman spectrum is beingobtained, the Raman signal is separated from any fluorescence signal.Both Raman and fluorescence spectra are then compared to existingcalibration spectra. After the calibration is performed, the spectra areanalyzed using any appropriate algorithm for spectral decomposition;non-limiting examples of such algorithms include Principal ComponentsAnalysis, Partial Least-Squares analysis, and spectral analysis using aneural network algorithm. This analysis provides the information neededto characterize the sample that was tested using the spectrometer. Theresults of the analysis are then presented to the user.

What is claimed is:
 1. A compact spectrometer system for obtaining aspectrum of a sample, comprising: an optical detector for detectinglight emanating from said sample; an optical filter located between saidsample and said detector to provide an angularly encoded spectrum; aFourier transform focusing element disposed between said optical filterand said detector; and a diffuser disposed between said sample and saidoptical filter, wherein the Fourier transform focusing elementtransforms the angularly encoded spectrum into a spatially encodedspectrum of light of different wavelengths, the spatially encodedspectrum arriving at a plurality of positions on the detector with eachof the plurality of positions on the detector correlated to a wavelengthof the spatially encoded spectrum.
 2. The compact spectrometer system ofclaim 1, wherein said optical filter comprises a plurality ofsub-filters with different center wavelengths, and wherein said opticalfilter comprises a plurality of substantially rectangular surface areas,each of which comprises a sub-filter.
 3. The compact spectrometer systemof claim 1, wherein said optical filter is chosen from the groupconsisting of (a) Fabry-Perot filter, (b) thin-film filter, and (c)interference filter.
 4. The compact spectrometer system of claim 1,further comprising a micro-lens array.
 5. The compact spectrometersystem of claim 4, wherein said micro-lens array is located in a focalplane of said Fourier transform focusing element.
 6. The compactspectrometer system of claim 4, wherein said detector is located at aplane substantially perpendicular to an optical axis such that themicro-lens array forms multiple images of said optical filter on saidoptical detector.
 7. The compact spectrometer system of claim 4, whereinsaid optical filter comprises a plurality of sub-filters with differentcenter wavelengths.
 8. The compact spectrometer system of claim 4,further comprising a second Fourier transforming focusing element,wherein said micro-lens array comprises an array of cylindrical lensesand is located at a focal plane of the Fourier transforming focusingelement and said optical detector is located at a focal plane of thesecond Fourier transform focusing element.
 9. The compact spectrometersystem of claim 1, further comprising a diffuser disposed between saidsample and said optical filter.
 10. The compact spectrometer system ofclaim 1, further comprising a light source adapted to illuminate saidsample.
 11. The compact spectrometer system of claim 10, wherein saidlight source is a laser.
 12. The compact spectrometer system of claim10, wherein said light source is a light-emitting diode.
 13. The compactspectrometer system of claim 10, further comprising a focusing systemadapted to focus light from said light source at a predeterminedlocation relative to said sample.
 14. The compact spectrometer system ofclaim 13, wherein said focusing system is an autofocus system.
 15. Thecompact spectrometer system of claim 13, wherein said focusing systemcontrols a position of a lens that focuses light produced by said lightsource onto said sample.
 16. The compact spectrometer system of claim13, wherein said focusing system controls optical properties of a lensthat focuses light produced by said light source onto said sample. 17.The compact spectrometer system of claim 13, wherein said focusingsystem comprises a voice-coil motor.
 18. The compact spectrometer systemof claim 13, wherein said focusing system comprises a piezoelectricmotor.
 19. The compact spectrometer system of claim 13, wherein saidfocusing system comprises a micro-electrical-mechanical-system (MEMS)motor.
 20. The compact spectrometer system of claim 1, furthercomprising means for communicating with a communication network.
 21. Thecompact spectrometer system of claim 20, wherein said communicationnetwork is a wireless communication network.
 22. The compactspectrometer system of claim 20, wherein said compact spectrometersystem is enclosed within a mobile communication device associated withsaid communication network.
 23. The compact spectrometer system of claim22, wherein said mobile communication device is a cellular telephone.24. The compact spectrometer system of claim 20, further comprising adatabase of spectral information in communication with saidcommunication network.
 25. The compact spectrometer system of claim 24,wherein said database is continuously updatable in real time.